Department of Oh-Oh, a continuing series

The explanation [of chevron deposits] is obvious to some scientists.  A large asteroid or
comet, the kind that could kill a quarter of the world’s population,
smashed into the Indian Ocean 4,800 years ago, producing a tsunami at
least 600 feet high, about 13 times as big as the one that inundated
Indonesia nearly two years ago.  The wave carried the huge deposits of
sediment to land.

Most astronomers doubt that any large comets
or asteroids have crashed into the Earth in the last 10,000 years.  But
the self-described “band of misfits” that make up the two-year-old
Holocene Impact Working Group say that astronomers simply have not
known how or where to look for evidence of such impacts along the
world’s shorelines and in the deep ocean.

Scientists in the working group say the evidence for such impacts
during the last 10,000 years, known as the Holocene epoch, is strong
enough to overturn current estimates of how often the Earth suffers a
violent impact on the order of a 10-megaton explosion.  Instead of once
in 500,000 to one million years, as astronomers now calculate,
catastrophic impacts could happen every few thousand years.

Here is the full story.  I should add there are reports that a tidal wave (not nearly of this size) may hit Japan today.  Here are our posts on asteroid deflection as a public good.